1. Field of the Invention
This invention relates to motor-operated press mechanisms, and more particularly to a motor-operated press mechanism which makes it possible to perform both a press working operation with an ordinary stroke and a die opening operation, for instance, in replacing a working die, and which is capable of adjusting the bottom dead center of the press ram.
2. Description of the Related Art
In the case where, in a motor-operated press machine of the crank press type, for instance the working die is replaced, it is necessary to adjust the bottom dead center of the press ram so as to obtain a predetermined working accuracy. The bottom dead center of the press ram is adjusted as follows: In an example of the bottom dead center adjustment method, a vertical movement shaft is threadably coupled to a slide, and the former is turned with respect to the latter, so that the slide is threadably adjusted in height (see Japanese Patent Unexamined Publication No. Hei 5-123900). In another example of the method, a crank shaft is variable in eccentric position, so that the adjustment is achieved by adjusting the amount of eccentricity (see Japanese Patent Unexamined Publication No. Hei 3-216296). In still another example of the method, the adjustment is achieved by changing the position of the fulcrum of a rocker arm adapted to push the ram (see Japanese Patent Unexamined Publication No. Hei 4-157098).
In the case where, in an ordinary press machine, its working metal mold is replaced, an upper die is removed from the press ram, and then the press ram is moved above so as not to obstruct the metal mold replacing operation; that is, the metal mold is replaced after the press ram has been retracted above. In a motor-operated press machine, the range of stroke of the press ram depends on the range of movement of the eccentric shaft of the crank. Hence, the range of stroke of the press ram is set to a relatively large value, and the metal mold is replaced after the press ram is moved to its uppermost position.
However, in a conventional motor-operated press machine, the range of stroke is set as required for a given press working operation. Hence, in replacement of the metal mold or during maintenance, the die opening operation cannot be readily achieved. In addition, the motor-operated press machine suffers from a difficulty that, in the case where the bottom dead center of the press ram is to be finely adjusted, the range of adjustment is small, and therefore the adjustment cannot be readily achieved.
Furthermore, the use of the motor-operated press machine of the type in which no clutch brake is used gives rise to another problem. That is, in the case where trouble occurs during press working--for instance a workpiece is erroneously fed to damage the die, it is impossible to stop the press machine immediately thereby to prevent the die from damage. That is, when such trouble occurs during press working, the press machine should be stopped without delay to eliminate the trouble. However, the inertia of the press ram or the like makes it impossible to stop the press machine immediately. In a resetting operation after the occurrence of jamming, correction cannot be manually made for the die, that is, it is impossible to put the operator's hand between the dies, with the result that the resetting operation takes time.